THE REACTIONS OF DROSOPHILA 



73 



TABLE I 



Showing the position of 5 flies in 14 trials, after having been in the dark box 

 one minute. At the beginning all the flies were in section 6. 85.71 per cent crept 

 to the uppermost third of the cylinder (sections 1 and 2). 



Number of Flies in the Different Sections of Cylinder 



After one minute the readings were taken. Eighty per cent of 

 the flies used in 50 trials went to the top section, 9 per cent 

 remained at the bottom and 11 per cent went to the middle. 

 Here also the flies responded negatively to gravity. 

 A set of records from this series is given in Table II. 



TABLE II 



Showing the position of 5 flies in 14 trials after having been one minute in the 

 light box with equal illumination at top and bottom. 78.57 per cent crept to the 

 uppermost third. 



Number of Flies in the Different Sections of Cylinder 



3. Effect of gravity on flies illuminated either from above or 

 below. — In order to study the effect of unequal illumination, a 



